This invention relates to recovery of the catalyst employed in a process for producing a 3-pentenoic ester which comprises reacting butadiene, carbon monoxide and an alcohol in the presence of a solvent and cobalt carbonyl or cobalt carbonyl complex catalysts.
Many processes for recovering the cobalt component from the reaction mixture obtained reacting butadiene, carbon monoxide and an alcohol have been proposed.
For example, two processes are disclosed in Japanese Patent Publication No. 7579/1975. In one (hereinafter called the extraction process) a cobalt component recovered from the reaction mixture obtained by reacting butadiene, carbon monoxide and an alcohol in the presence of a cobalt carbonyl catalyst or a cobalt carbonyl complex catalyst by extracting a 3-pentenoic ester from the reaction mixture which paraffins, such as cyclohexane or pretroleum ether and circulating the resulting cobalt carbonyl complex catalyst. In the other (hereinafter referred to as the distillation process), a cobalt component is recovered from the reaction mixture obtained by reacting butadiene, carbon monoxide and an alcohol in the presence of a cobalt carbonyl catalyst or a cobalt carbonyl complex catalyst by distilling a 3-pentenoic ester from the reaction mixture and circulating the resulting cobalt carbonyl complex.
However, though the ratio of recovery of the cobalt carbonyl catalyst is high in the first recovering procedure of the extraction process, the more the catalyst is used, the more easily it is transferred into the paraffin phase, so, with repeated use, the efficiency of recovery of the catalyst becomes very low.
In the distillation process, all the cobalt carbonyl complex catalyst employed can be recovered. However, when the catalyst is used repeatedly, activity of the catalyst is lowered and high boiling substances derived from polymerization of butadiene accumulate in the catalyst. This is not desirable.
The above prior processes for recovering a cobalt carbonyl complex catalyst from the reaction mixture obtained by reacting butadiene, carbon monoxide and an alcohol in the presence of the cobalt carbonyl complex catalyst have the following shortcomings:
(1) When the catalyst is used repeatedly, it is difficult to maintain the activity of the catalyst at a high level; and PA0 (2) It is difficult to recover all the catalyst from the reaction mixture. Therefore, recovery of the cobalt carbonyl complex catalyst can not be effected on an industrial scale.
In oxo synthesis using a cobalt carbonyl catalyst, the cobalt component employed can be recovered in the form of organic or inorganic acid salts, hydroxide and basic carbonate from the reaction mixture obtained by the oxo synthesis. In this case either of two processes is used. In one process (hereinafter referred to as aqueous extraction process) the reaction mixture is contacted with an aqueous solution of an acid or a salt, thereby extracting the cobalt component from the oil phase with the aqueous phase. In other process (hereinunder referred to as the precipitation process) the cobalt from the reaction mixture is precipitated by thermal decomposition, contacting the cobalt carbonyl with an aqueous acid solution to recover cobalt, and then the cobalt is recovered by alkaline treatment.
However, the processes for recovering cobalt from the reaction mixture obtained in the oxo synthesis by aqueous extraction process are improper for hydroesterification of butadiene because tertiary amines, such as pyridine or isoquinoline are used in the hydroesterification of butadiene. That is, to avoid the reaction of the acid with the tertiary amine the aqueous extraction process can not be applied to the hydroesterification of butadiene.
In the precipitation process, cobalt carbonyl is precipitated by thermal decomposition, and then organic solvents are recovered from the mixture containing the cobalt carbonyl by distillation. The cobalt is recovered by contacting the resulting residue with an aqueous acid solution. In this case, however, since the residue contains tarry or solid high boiling point substances, the ratio of recovered cobalt becomes very low.
On the other hand, 20 times as much cobalt is used in the hydroesterification reaction of butadiene, as in the oxo synthesis. Therefore, it is important to increase the recovery ratio of recovered cobalt in the hydroesterification reaction of butadiene.